It appears to me she's molting, and it's normal. All of them probably are, as are everyone's chickens who live in the Northern Hemisphere. When daylight grows shorter, it triggers hormones that cause chickens to lose their feathers. Some all at once, some a little at a time. New feathers grow in, so that they have a nice new fluffy coat before winter. I could make a feather bed with all the fluff currently blowing around in my coop, run and yard. You should check out the current contests on BYC, there's one for best pic for molting chickens. It's an eye-opener if you've never seen a chicken molt before!
Handle them gently, as their skin is pretty sensitive right now.